Inorganic fiber paper is lightweight, has a good handling capability, and exhibits excellent heat resistance. Therefore, inorganic fiber paper is used as a heat-resistant seal material, for example. In recent years, it has been pointed out that health problems may occur due to inhalation of inorganic fibers into a lung of a living body. Therefore, biosoluble inorganic fibers that do not cause (or rarely cause) health problems upon inhalation have been developed (see JP-A-2002-068777, for example).